New technologies are continuously being developed to improve energy efficiency. One such technology is the use of infrared reflective pigments in coatings positioned on a building's (or other object's) exterior. As one is aware, the sun emits about 50% of its energy as near-infrared radiation. When this near-infrared radiation is absorbed, it is physically converted into heat. Coatings containing infrared reflective pigments work by reflecting away sunlight and by blocking the transfer of heat thereby reducing the heat load to the building. For example, white pigments, such as titanium oxide, have been used in coatings to reflect a majority of the sun's energy. Oftentimes, it's desirable to provide a colored coating in place of white for aesthetic reasons. However, the selection of pigments that are available for use is limited since they tend to absorb more of the sun's energy than is desired leading to a marked reduction in the above-described effect. Thus, various systems have been and continue to be tried to provide colored coatings having improved solar reflectance.
For example, U.S. Pat. No. 5,540,998 describes a system in which two or more non-white pigments having particle diameters of 50 μm or less are combined to yield a color of low lightness, and in particular, achromatic black. U.S. Pat. No. 5,962,143 further describes a dark colored coating that contains one or more black pigments, one or more non-white pigments and silicic acid.
In U.S. Pat. No. 6,174,360, the use of complex inorganic colored pigments (CICP's) in coatings are taught to exhibit dark drab colors in the visible portion along with reflectivity in the near-infrared portion of the electromagnetic spectrum.
U.S. Pat. No. 6,336,397 describes an infrared reflective system containing two or more layers with one layer containing a resin and pigment which provides the desired color and another layer containing a pigment which provides infrared reflectance. U.S. Pat. Publ. No. 2009/0268278 also discloses a two layer sheet-like infrared reflective system having a top layer consisting of a synthetic resin and an organic pigment laminated onto a bottom layer consisting of a synthetic resin and a titanium oxide-based white pigment. WO 04/094539 further discloses a layered system having a primer layer which is lighter in color and more reflective than a basecoat layer.
In addition, U.S. Pat. No. 6,521,038 teaches a near-infrared reflecting composite pigment containing a near-infrared non-absorbing colorant and a white pigment that is coated with such a colorant. The composite pigment may then be used as a coloring agent in coatings.
Finally, WO 2009/136141 describes the use of near-infrared-scattering particulate material which provides high reflection of near-infrared radiation and diminished reflectance of visible light in combination with various colorants.
Although each provide solar reflectance, some of the disadvantages in using these currently available systems include: they provide relatively pale coloring since a high level of conventional titanium dioxide is needed to give the desired level of solar reflection; impurities contained within the systems can lead to absorptions in the near-infrared part of the spectrum resulting in a reduction of solar reflectance; and primer layers are not engineered to give maximum solar reflectance. As such, alternative systems which exhibit enhanced solar reflectivity in a wide range of dark or more intense uniform colors than is otherwise achievable is still highly desirable.